First-principles prediction of a two-dimensional vanadium carbide (MXene) as the anode for lithium ion batteries

Abstract

MXene V2C structure provides a specific theoretical capacity as high as 472 mA h g−1 at the Li2V2C stoichiometry and extremely fast diffusion with an energy barrier less than 0.1 eV. These intriguing findings are robust against intrinsic structural defects.

Strategies for Fabricating High‐Performance Electrochemical Energy‐Storage Devices by MXenes

“…[199] The energy barriers for the second lithium ion diffusing along H c -B-H c and H c -H v -H c on the V 2 C surface with an occupied V V site were calculated to be 0.032 and 0.02 eV, as shown in Figure 18 (d) and (e). [199] Compared with defect-free V 2 C, the one with vanadium vacancies displayed a stronger binding ability to lithium ions (evidenced by a 30 % increase in binding energy) and slightly better diffusion kinetics (illustrated by a reduction in diffusion energy barrier by 0.002 eV). [167,199] Oppositely, Wu et al suggested that the presence of transition metal vacancy in Mo 2 C might have a minor negative influence on the rate performance of lithium-ion batteries.…”

“…Thus, it is believed that the incorporation of vacancies might modify the charge storage capability of 2D nanomaterials, such as MXenes. [198] Defect engineering of MXenes has been studied theoretically, including the influence of termination vacancies (À Cl deficiency on the surface of Ti 3 C 2 Cl 2 ), [196] carbon vacancies (in V 2 C) [199] as well as transition metal vacancies (in Mo 2 C) [200] on the electrical properties of the corresponding MXenes. Experimentally, defective MXenes could be prepared by selectively etching A layers and metal elements in quaternary solid-solution MAX phase (such as (Nb 2/3 Sc 1/3 ) 2 AlC) or ordered quaternary MAX phases ((Mo 2/3 Sc 1/3 ) 2 AlC).…”

“…[196] In addition to the vacancies of functional groups, the effect of vanadium and carbon vacancies (denoted as V V and V C , respectively) in V 2 C MXenes (as shown in Figure 18 (c)) on the binding and diffusion behaviour of lithium ions was explored. [167,199] It was found that the binding energy of lithium ions for V v was higher than that for V C (3.13 versus 2.40 eV), suggesting that the adsorption of lithium ions on V v was more thermodynamically favourable. [199] The energy barriers for the second lithium ion diffusing along H c -B-H c and H c -H v -H c on the V 2 C surface with an occupied V V site were calculated to be 0.032 and 0.02 eV, as shown in Figure 18 (d) and (e).…”

“…[167,199] It was found that the binding energy of lithium ions for V v was higher than that for V C (3.13 versus 2.40 eV), suggesting that the adsorption of lithium ions on V v was more thermodynamically favourable. [199] The energy barriers for the second lithium ion diffusing along H c -B-H c and H c -H v -H c on the V 2 C surface with an occupied V V site were calculated to be 0.032 and 0.02 eV, as shown in Figure 18 (d) and (e). [199] Compared with defect-free V 2 C, the one with vanadium vacancies displayed a stronger binding ability to lithium ions (evidenced by a 30 % increase in binding energy) and slightly better diffusion kinetics (illustrated by a reduction in diffusion energy barrier by 0.002 eV).…”

“…[199] Compared with defect-free V 2 C, the one with vanadium vacancies displayed a stronger binding ability to lithium ions (evidenced by a 30 % increase in binding energy) and slightly better diffusion kinetics (illustrated by a reduction in diffusion energy barrier by 0.002 eV). [167,199] Oppositely, Wu et al suggested that the presence of transition metal vacancy in Mo 2 C might have a minor negative influence on the rate performance of lithium-ion batteries. [200] As shown in Figure 18 (f) and (g), it was reported that the energy barrier for lithium ions to leave Mo vacancies was large (> 0.9 eV), and this trapping effect might hinder the delithiation process.…”